This application claims the priority of Japanese Patent Application No. 248718/1991 filed Aug. 30, 1991, which is incorporated herein by reference.
Diamond is endowed with wide applications. In general, diamond tools have been made from sintered diamond polycrystalline diamond hitherto. Besides tools, diamond is going to be utilized as a material or semiconductor for making electronic devices. Such diamond as a material for electronic devices requires to be a single crystal. Polycrystalline diamond is useless in the field of electronic devices, because grain boundaries in polycrystals reduce the mobility of carries and prevent the formation of a good pn-junction. Since a polycrystal is an assembly of a plurality of small single crystals, contains many grain boundaries which are surfaces of the small single crystals. Grain boundaries scatter electrons and holes and impair pn-junctions, for example low breakdown voltage in a reverse direction, high resistance in a forward direction. Elimination of such bad effects caused by grain boundaries of polycrystals requires an epitaxial growth of diamond.
Only a single crystal diamond substrate allows the growth of a diamond film epitaxially thereon. This is homoepitaxy. There Is no problem of lattice mismatch due to the difference of lattice constants or difference of thermal expansion coefficients. However, a diamond substrate itself is expensive and difficult to produce. It will be indispensable to grow a diamond film on another material besides diamond for responding to wide applications of diamond. However, it is difficult to grow a diamond film epitaxially on a material different from diamond. The difficulty of heteroepitaxy (epitaxial growth on a non-diamond material) is a great problem to be solved for exploiting excellent properties of diamond.
At present, no report: except a heteroepitaxy on a c-BN substrate by Suzuki has been issued so far. SUZUKI et al., THE THIRD DIAMOND SYMPOSIUM, 1989 proceeding text, p75.
Suzuki reported that a diamond is epitaxially grown on a c-BN (cubic boron nitride) substrate. This was a first success of heteroepitaxy of diamond. However, a c-BN substrate is not easily produced. Synthesis under high pressure is only an applicable method for producing a c-BN substrate at present. The synthesis of c-BN is as difficult as that of diamond. Thus, the heteroepitaxy on a c-BN substrate is not a practical method of producing an epitaxial diamond film. The diamond/c-BN heteroepitaxy was not a breakthrough in epitaxy of diamond. Even now there is no practical, useful method of growing diamond epitaxially on a practical substrate which can be easily obtained at low costs.
Fujita et al. reported a nickel (Ni) substrate to grow an assembly of diamond islands epitaxially thereon. Nickel has a lattice constant similar to that of diamond. FUJITA et al., THE FOURTH DIAMOND SYMPOSIUM, 1991, proceeding text. p13.
However, Fujita's diamond was not a compact film. It was essentially an assembly of islands of diamond. The epitaxy meant that the crystallographical direction of the islands coincided with that of the substrate. Many diamond islands were sparsely populated on a (001)Ni substrate or a (111)Ni substrate in Fujita's diamond fi Ira.
Further deposition on the islands would not result in a hole-free film. The reason is that erosion of diamond by the nickel substrate is inevitable during further deposition. No compact film of diamond could be obtained by the further deposition. The sparsely populated islands did not mean the shortage of deposition. The further deposition would force the initially epitaxially grown islands to vanish in the substrate. Although nickel is one of the most favorable materials for a substrate of diamond epitaxy because of the lattice constant being nearly equal to that of diamond, a nickel substrate does not allow depositing a compact diamond film thereon.
In the long run, diamond is the most suitable material for a substrate of diamond epitaxy. Synthesis of a wide diamond single crystal is difficult at present. But poly-crystalline diamond can be easily synthesized by the technology of the state of art. Gels proposed a method for producing diamond films which have nearly the same crystallographical direction by arraying small diamond single crystals in a common direction, and synthesizing diamond films on the arranged small diamond granules having the same crystallographical direction. M. W. GEIS & H. I. SMITH; SPRING MEETING OF ELECTROCHEMICAL SOCIETY, WASHINGTON, D.C.
Gels et al. dicloses a method to make a compact mosaic diamond film having the same direction. But it is very difficult to exclude grain boundaries with a small angle of some 1 degree in Geis's method.
In order to solve the above problems, this invention has been devised. A purpose of this invention is to provide a wide, compact diamond film having a good crystallographical property and an aligned crystallographical direction. Another purpose of this invention is to provide a method of producing a wide, compact diamond film having a good crystallographical property. Another purpose of this invention is to provide a low cost method for producing a wide, compact diamond film. Another purpose of this invention is to provide a method of epitaxial growth of diamond without using a diamond substrate.